Experimental insights into strut-induced enhancement of fuel spreading and flow structures in a supersonic cavity flameholder

This study investigates flow–fuel interactions in a supersonic cavity flameholder under Mach 2 inflow conditions, with the objective of enhancing fuel spreading outside the cavity. A baseline configuration featuring a half-section centerbody, a backward-swept strut, and a cavity flameholder is examined and compared with three modified designs. Schlieren imaging, fuel injection, and particle image velocimetry were used to characterize shock structures, fuel distribution, and velocity fields, respectively. The results show that all three modified configurations promote more effective fuel transport out of the cavity. In particular, the configuration with the strut relocated downstream and aligned flush with the cavity front wall achieves the widest fuel spreading and the largest grayscale difference in the schlieren images, suggesting enhanced fuel atomization, due to reduced resistance to expansion and enhanced fuel–air contact. While outward cavity flow enhances fuel spreading, it simultaneously displaces the shear layer outward, decoupling it from the in-cavity fuel and potentially compromising shear-induced atomization and air entrainment essential for stable combustion. Additionally, the results indicate that the size of the recirculation zone is not necessarily beneficial when maximized, as overly strong reverse flow can impede fuel spreading. These findings demonstrate that effective strut-cavity flameholder design requires strategic control of shear layer position, as strength alone cannot ensure balanced fuel spreading, atomization, and cavity–freestream mass exchange. The study proposes design strategies for enhancing fuel–air mixing in strut-cavity flameholders and offers insights applicable to practical engineering applications.